Wafer level chip scale package having varying thicknesses

ABSTRACT

A wafer level chip scale package (WLCSP) with portions that have different thicknesses. A first passive surface of a die in the WLSCP includes a plurality of surfaces. The plurality of surfaces may include inclined surfaces or flat surfaces. Thicker portions of die, with more semiconductor material remaining are non-critical portions that increase a WLCSP&#39;s strength for further processing and handling after formation, and the thinner portions are critical portions that reduce a Coefficient of Thermal Expansion (CTE) mismatch between a WLCSP and a PCB.

BACKGROUND Technical Field

The present disclosure is directed to a Wafer Level Chip Scale Package(WLCSP) with a thickness that varies.

Description of the Related Art

Generally, WLCSP are manufactured by coupling solder balls to an activeside of a semiconductor wafer. The solder balls are then coupled to anadhesive tape to support the wafer during singulation into individualWLCSP. The wafer is then singulated into individual WLCSP throughsawing, cutting, etching, or some other singulation technique. After thewafer has been singulated, the singulated WLCSPs are removed from theadhesive tape. These individual WLCSPs may be coupled to a printedcircuit board (PCB) for use and mounting within an electronic device.

As the demand for manufacturing smaller sized and lower profiledsemiconductor packages increases for smaller and lower profiledelectronics, there are significant challenges to produce WLCSPs withhigh pin counts, smaller sizes, and lower profiles.

One significant challenge in producing smaller sized and lower profiledWLCSPs, is achieving high Board Level Reliability (BLR) againsttemperature cycling on board (TCOB) due to mismatches of coefficients ofthermal expansion (CTE) between a WLCSP and a PCB. Generally, the PCBhas a much higher CTE than the WLCSP. This CTE mismatch between the PCBand the WLCSP can result in damage to the WLCSP and electroniccomponents in the WLCSP that can cause the WLCSP to fail or reduce inefficiency. The life expectancy of the WLCSP due to temperature cyclingis significantly reduced because of this CTE mismatch between the WLCSPand the PCB.

Another significant challenge is processing and handling smaller andthinner WLCSPs. The thinner WLCSPs are more susceptible to damage causedby external stresses and forces. For example, small external forces suchas dropping the WLCSP during handling, shifting during shipment, rapidchanges in temperature, or other such similar external forces orstresses may cause significant damage to the small and thin WLCSP.

BRIEF SUMMARY

The present disclosure is directed to various wafer level chip scalepackages (WLCSP) that have critical portions that are thin andnon-critical portions that are thicker than the critical portions. Inthis context, critical describes portions of a die of the WLCSP wherethe die is likely to bend or flex due to heat or thermal exposure thatcan result in damage to the die or components within the die. Thenon-critical portions describe areas where the die is not likely to bendor flex due to heat or thermal exposure. These thin portions reduce theCTE mismatch between the WLCSP and a printed circuit board (PCB)increasing the board level reliability (BLR) of the WLCSP againsttemperature cycling on board (TCOB). In addition, the thicker portionsallow for further processing and handling of the WLCSP such as pick andplace for coupling the WLCSP to the PCB. This WLCSP with thinnerportions and thicker portions can be manufactured using semiconductormanufacturing techniques such as utilizing an adhesive tape, etchingtechniques, and singulating techniques.

According to one embodiment of a WLCSP, the WLCSP includes a die,passivation layers, redistribution layers (RDL), under bumpmetallizations (UBM), and solder balls coupled to the UBMs. The WLCSPincludes a first surface that is passive and a second surface that isaround the first surface, the second surface also being passive. TheWLSCP includes a third surface opposite to the first and secondsurfaces, the third surface being active. The first surface is furtherfrom the third surface than the second surface. A fourth surface extendsfrom the first surface to the second surface. The third surface includescontact pads or UBMs. In addition, solder balls are coupled to thecontact pads or UBMs on the third surface. Sidewalls extend between thesecond surface and the third surface.

This embodiment of the WLCSP further includes a first portion, a secondportion, and a third portion. The first portion has a first thicknessthat extends between the third surface and the first surface. The secondportion has a second thickness that extends between the third surfaceand the second surface. The third portion has a third thickness thatextends between the third surface and the fourth surface. The firstthickness of the first portion is greater than the second thickness ofthe second portion. The first portion and the second portion areseparated from and coupled to each other by the third portion. The thirdthickness of the third portion varies between the second thickness andthe first thickness. The fourth surface extends from the second surfaceto the first surface at an incline. The first portion being thicker thanthe second portion means that the first portion extends in an outwarddirection from the second surface of the WLCSP. The first portion is acritical portion, the second portion is a non-critical portion, and thethird portion is a transition portion. The first portion is positionedat a center of the WLCSP and is surrounded by the second portion and thethird portion. The critical portions include features that aresusceptible to damage in response to stresses or thermal exposure thatcause flexing, bending, or other similar distortions.

In this embodiment, the thicker non-critical portion makes the WLCSPstronger at a center of the WLCSP allowing for further processing andhandling, such as picking and placing the WLCSP on a PCB or shipping theWLCSP. In other words, this thicker non-critical portion allows for theWLCSP to have a greater resistance against external forces because thenon-critical portions are thicker. This increase in strength andthickness reduces the likelihood of damage to the WLCSP caused byexternal stresses and forces during further handling, processing,shipping, or other similar processes.

In this embodiment, the thinner critical portion reduces a CTE mismatchbetween the PCB and this embodiment of the WLCSP when the WLCSP ismounted to the PCB. This reduction in the CTE mismatch between the PCBand this embodiment of the WLCSP improves the BLR of the WLCSP byincreasing the WLCSP's tolerance to TCOB. This embodiment of the WLCSPis more tolerant to bending, warping, expansion, and contraction in thePCB and the WLCSP due to changes in temperature that the WLCSP and thePCB are exposed because when the WLCSP and the PCB have similar CTEs,the WLCSP and the PCB bend or flex in a similar ways.

In an alternative embodiment of the WLCSP above, the fourth surface thatseparates the second surface and the third surface may be verticalinstead of inclined.

In another alternative embodiment, a WLCSP may have a first surface, asecond surface, and a third surface opposite a fourth surface thatincludes contacts. The second surface extends from the first surface toa first sidewall, and the third surface extends from the first surfaceto a second sidewall. The second surface and the third surface are at anincline in this embodiment, which results in the WLCSP having a secondportion and a third portion with varying thicknesses. In addition, theWLCSP in this embodiment includes a first portion with a consistentthickness that separates and couples the second portion to the thirdportion. The first portion is located between the first surface and thefourth surface of the WLCSP.

In another alternative embodiment of the WLCSP, a first portion extendsin an outward direction from a surface of the WLCSP and has a plusshape. In this alternative embodiment, the corners of the WLCSP arethinner than the first portion with the plus shape. In addition, thefirst portion is positioned at the center of the WLCSP and extends fromone sidewall to another opposite sidewall.

In another alternative embodiment, a plurality of thicker portions mayextend in an outward direction from a surface of the WLCSP. Theplurality of thicker portions may have any shape. In addition, thisalternative embodiment of the WLCSP may include thinner portions thatare aligned with trenches, gaps, or spaces that extend between and passby the plurality of thicker portions. The thinner portions include afirst group of thinner portions that extend in a first direction, and asecond group of thinner portions that extend in a second direction thatis transverse to the first direction.

The above embodiment and alternative embodiments of a WLCSP with thinnerportions and thicker portions are manufactured by a method that includescoupling a wafer to an adhesive tape, etching the wafer, singulating thewafer into individual WLCSPs, and removing the individual and singulatedWLCSP.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical references numbers identify similar elementsor acts unless the context indicates otherwise. The sizes and relativeportion of the elements in the drawings are not necessarily drawn toscale.

FIG. 1A is a top plan view of an embodiment of a WLCSP;

FIG. 1B is a side plan view of the embodiment of the WLCSP in FIG. 1A;

FIG. 1C is a cross-sectional view taken along line 1C-1C in FIG. 1A;

FIG. 1D is bottom plan view of the embodiment of the WLCSP in FIGS. 1Aand 1B;

FIG. 1E is cross-sectional view of the embodiment of the WLCSP in FIG.1A taken along line 1E-1E in FIGS. 1A, 1B, and 1D;

FIGS. 2A-2C are alternative embodiments of a WLCSP;

FIG. 3A is a top plan view of an alternative embodiment of a WLCSP;

FIG. 3B is a side plan view of the alternative embodiment of the WLCSPin FIG. 3A;

FIG. 4 is a top plan view of an alternative embodiment of a WLCSP;

FIG. 5A is a top plan view of an alternative embodiment of a WLCSP;

FIG. 5B is a cross-sectional view of the alternative embodiment of theWLCSP in FIG. 5A taken along line 5B-5B in FIG. 5A;

FIG. 6 is a top plan view of an alternative embodiment of a WLCSP;

FIG. 7 is a flow chart diagram of a method of manufacturing according tothe embodiments disclosed; and

FIGS. 8A-8E are side plan views of successive steps of a packagefabrication process according to the embodiments disclosed.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thedisclosure. However, one skilled in the art will understand that thedisclosure may be practiced without these specific details. In otherinstances, well-known structures associated with electronic componentsand fabrication techniques have not been described in detail to avoidunnecessarily obscuring the descriptions of the embodiments of thepresent disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising,” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

The use of ordinals such as first, second and third does not necessarilyimply a ranked sense of order, but rather may only distinguish betweenmultiple instances of an act or structure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

The present disclosure is directed to a Wafer Level Chip Scale Package(WLCSP) that includes multiple thicknesses on a passive side of a die.For example, FIGS. 1A-1E are directed to one embodiment of a WLCSP 100including a die 132 that has a first surface 110, a second surface 112,and a third surface 114 on a first side of the die, which is a passiveside of the die. The die 132 includes a fourth surface 116 on a secondside of the die, the second side being opposite the first side and beingan active side of the die 132. The die includes a substrate, likely ofsemiconductor materials like silicon, silicon germanium, or othersuitable materials. The die 132 includes sidewalls 118 extending fromthe fourth surface 116 to the first surface 112 of the die 132. Thefourth surface 116 of the die 132 includes Under Bump Metallizations(UBMs) 120 and solder balls 122 coupled to the UBMs 120. Aredistribution layer (RDL) 131 is positioned between the die 132 and theUBMs 120. The die 132 is a silicon material or other suitablesemiconductor material. Transistors, resistors, capacitors and othercircuitry may be formed in the die 132 with electrical connections thatextend to the active side of the die. The passive side of the die doesnot include any electrical components on the surfaces furthest from theactive side of the die.

In this embodiment, the first surface 110, the second surface 112, andthe fourth surface 116 are opposite the third surface 114 as shown inFIG. 1A. The die 132 has different thicknesses between the differentsurfaces. The first surface 110 of the WLCSP 100 is positioned at thecenter of the die 132 and has a square shape as shown in FIG. 1A, withsides of the square being substantially parallel to respective sides ofthe die. However, in alternative embodiments, the shape of the firstsurface can be a circle, an oval, a triangle, a diamond, or any othershape. See FIGS. 2A-2C. Also, in alternative embodiments, the firstsurface 110 may be positioned at a different location on the WLCSP 100instead of at the center of the WLCSP 100.

The fourth surface 116 surrounds the first surface 110 and is positionedbetween the first surface 110 and the second surface 112. The secondsurface surrounds the first surface 110 and the fourth surface 116 andis positioned between the fourth surface 116 and the sidewalls 118. Thefourth surface 116 extends between the first surface 110 and the secondsurface 112. The fourth surface 116 separates the first surface 110 fromthe second surface 112. The fourth surface 116 is transverse to thefirst surface 110, the second surface 112, and the third surface 114.The fourth surface 116 may be at an incline as shown in FIG. 1B.However, in alternative embodiments, the fourth surface 116 may bevertical or substantially perpendicular to the second surface.

The third surface 114 is opposite the first surface 110 and the secondsurface 112, and the fourth surface 116 is a front side surface orotherwise an active surface where electrical contacts are formed. Thefirst surface 110, the second surface 112, and the fourth surface 116are a back side surface or otherwise a passive surface that has noelectrical contacts. It is possible that there may be a through siliconvia or other contact formed to extend to this passive surface. Thesidewalls extend between the second surface 112 and the third surface114. The sidewalls 118 have a first height H1.

The UBMs 120 are on the third surface 114 as shown in FIGS. 1B-1D. Theplurality of solder balls 122 are coupled to the UBMs 120 on the thirdsurface 114. Each respective solder ball 122 is coupled to its ownrespective UBM 120. The UBMs are illustrated as round in FIG. 1D,however, these UBMs may be square or rectangular or any other suitableshape. The solder balls 122 are utilized to couple the WLCSP 100 to aPCB or to other electronic components within an electronic device suchas a smart phone, a tablet, a computer, a calculator, or any othersimilar electronic device. As shown in FIG. 1D, the plurality of UBMs120, which may be a plurality of contact pads, bond pads, or some otherelectronic coupling location, and a plurality of solder balls 122 are ina Ball Grid Array (BGA) configuration on the third surface 114 of theWLCSP 100.

The WLCSP 100 includes a plurality of portions 125, 127, 129 as shown inFIGS. 1A-1C. The plurality of portions includes a first portion 125, asecond portion 127, and a third portion 129. The first portion 125 islocated between the first surface 110 and the third surface 114 and hasa first thickness T1 that extends between the first surface 110 and thethird surface 114. The second portion 127 is located between the secondsurface 112 and the third surface 114 and has a second thickness T2 thatextends between the second surface 112 and the third surface 114. Thethird portion 129 is located between the third surface 114 and thefourth surface 116 and has a third thickness T3 that extends between thethird surface 114 and the fourth surface 116.

The third thickness T3 is a variable thickness that varies between thefirst thickness T1 and the second thickness T2. The first thickness T1of the first portion 125 is greater than the second thickness T2 of thesecond portion 127. The second portion 127 surrounds the first portion125 and the third portion 129 of the WLCSP 100. The second portion 127is thinner than the first portion 125 and forms a perimeter or aboundary around the first portion 125 and the third portion 129. Thesecond portion 127 is positioned adjacent to and along the sidewalls118. The first portion 125 is positioned at the center of the WLCSP 100.The third portion 129 surrounds the first portion 125 and separates andcouples the first portion 125 to the second portion 127. The thirdportion 129 acts as a transition portion between the first portion 125and the second portion 127. The first portion 125 is a non-criticalportion and the second portion 127 is a critical portion. This criticalportion is a location where bending and flexing can result due to heator thermal exposure. This heat or thermal exposure that results inbending and flexing can cause cracks in the die 132, mechanical failuresof electrical components in the die 132, or short circuiting betweenelectrical components in the die 132.

The first thickness T1 of the non-critical portion 125 may be 200-400microns and the second thickness T2 of the critical portion 127 may be100-150 microns. However, in other alternative embodiments, thethicknesses of the non-critical portion 125 and the critical portion 127may have different values than those discussed directly above. The firstsurface 110, which is shaped like a square may have a 2×2 mm area.However, in other alternative embodiments, the first surface may have anarea with different dimensions.

A benefit of the WLCSP 100 of the present disclosure is when furtherprocessing or shipping this embodiment of the WLCSP 100, thenon-critical portion 125, which is thicker than the critical portion127, causes the WLCSP 100 to be stronger and more resistant to externalstresses and forces at the center because the WLCSP is thicker at thecenter. The more stress and force resistant center of the WLCSP 100 atthe non-critical portion 125 allows for the WLCSP 100 to be picked up atthe non-critical portion 125 and placed on a PCB, placed in a shipmentcontainer, or shipped to a customer while reducing the likelihood ofdamage caused by external stresses or forces. These external stresses orforces are those that the WLCSP 100 is exposed to during the aboveprocesses or other similar processes. The non-critical portion 125 alsoincreases the stress resistance of the WLCSP 100 when it is mountedwithin an electronic device as well because of the non-criticalportion's 125 greater resistance to external forces.

An alternative benefit of the WLCSP 100 of the present disclosure iswhen a WLCSP 100 is mounted or coupled to a PCB, the critical portion127 of the WLCSP 100, which is thinner than the non-critical portion125, reduces a difference between a first coefficient of thermalexpansion (CTE) of the WLCSP 100 and a second CTE of the PCB because theWLCSP 100 is thinner at the critical portion 127 than the non-criticalportion 125. By reducing this difference between the first CTE and thesecond CTE, which may be called a CTE mismatch, when the WLCSP 100 andthe PCB are mounted within an electronic device and exposed to changesin temperature that are rapid or slow, the WLCSP 100 and the PCB willexpand, warp, contract, and bend in similar ways. This similarity inexpansion, contraction, warping, and bending will reduce damage thatresults from the PCB expanding more quickly or slowly than the WLCSP 100and vice versa. By reducing the CTE mismatch between the WLCSP 100 andthe PCB, the board level reliability (BLR) of the WLCSP 100 when exposedto temperature cycling on board (TCOB) is increased causing the lifespan of the WLCSP 100 to be longer. This reduction in the CTE mismatchalso reduces the chance of damage that could cause a failure or reduceefficiency of the WLCSP 100 or the PCB when in use in an electronicdevice due to temperature changes.

An alternative benefit of the WLCSP 100 of the present disclosure isthat the non-critical portion 125 and critical portion 127 allow for theWLCSP 100 to be made even thinner.

Even though these benefits are not discussed with respect to each andevery embodiment or alternative embodiment of a WLCSP with varyingthicknesses of the present disclosure, these benefits apply to each andevery embodiment of a WLCSP disclosed in the present disclosure.

FIG. 1E is an enhanced view of the die 132 through cross section 1E-1Ein FIGS. 1A, 1B, and 1D. The WLCSP 100 includes the die 132 having aplurality of bond pads or contact pads 130 that are coupled to a varietyof active and passive circuitry in the die (not shown). In addition, theWLCSP 100 includes a redistribution layer (RDL) 131 that includes afirst dielectric layer 124, a conductive layer 126, and a seconddielectric layer 128. The RDL 131 couples the bond pads 130 from the dieto the UBMs 120 and ultimately to the outside world. The UBMs 120 arecoupled to the RDL 131 and the solder balls 122 is coupled to the UBMs120.

The bond pads 130 are electrically coupled to the RDL 131 and the RDL131 is electrically coupled to the UBMs 120. The first dielectric layer124 of material is positioned between the die 132 and the conductivelayer 126. The first dielectric layer 124 may be a polyimide layer, apassivation layer, or some other layer of non-conductive or insulatingmaterial. The conductive layer 126 may be a copper material, a goldmaterial, a metal alloy, or some other conductive material. The seconddielectric layer 128 of material is positioned between the conductivelayer 126 and the UBMs 120. The second dielectric layer 128 may be apolyimide layer, a passivation layer, or some other layer ofnon-conductive or insulating material. The solder balls 122 are coupledto the UBMs 120 as discussed earlier with respect to FIGS. 1B and 1D.

The bond pads 130 of the die 132, the conductive layer 126, the UBMs120, and the solder balls 122 are electrically coupled together. Thebond pads 130, the conductive layer 126, the UBMs 120, and the solderball 122 can be used to electrically couple the die 132 to otherexternal electronic components or semiconductor components such asanother semiconductor die, a PCB, or some other electronic device thatthe WLCSP 100 may be mounted or coupled. The solder balls 122 alsophysically couple the WLCSP 100 to an external electronic orsemiconductor component.

The first dielectric layer 124 positioned between the die 132 and theconductive layer 126 electrically isolates bond pads 130 and portions ofthe conductive layer 126 from other respective bond pads 130 andrespective portions of the conductive layer 126 to avoid cross talkbetween bond pads 130 and portions of the conductive layer 126. Crosstalk occurs when two electronic components within a WLCSP becomeelectrically coupled to one another due to a defect or damage in theWLCSP, which can reduce efficiency of the WLCSP, cause the WLCSP tocompletely fail, or reduce the WLCSP's life span.

The second dielectric layer 128 positioned between the UBMs 120 and theconductive layer 126 electrically isolates portions of the conductivelayer 126 and UBMs 120 from other respective portions of the conductivelayer 126 and UBMs 120 to avoid cross talk between portions of theconductive layer 126 and UBMs 120. This is similar to how the firstdielectric layer 124 isolates the bond pads 130 and portions of theconductive layer 126 from other bond pads 130 and portions of theconductive layer 126 as discussed earlier with respect to the firstdielectric layer 124. The second dielectric layer 128 also helps in theformation of the UBMs 120, which will be discussed directly below.

The first dielectric layer 124, the conductive layer 126, and the seconddielectric layer 128 are formed by a plurality of etching and maskingsteps. The first dielectric layer 124 may be formed by first placing apassivation material on of the die 132. After placing the passivationmaterial, a mask material is placed on the passivation material leavingcertain areas of the passivation material exposed and covering otherareas of the passivation material. The mask material may be aphotoresist mask, a hard mask, or some other mask material. After themask material is placed, the passivation material is etched. Thisetching may be a chemical etching, a plasma etching, a radiationetching, or some other etching technique. The mask material protects theportions of the passivation layer that it covers from being removed.After the etching step is complete, the mask material is removed leavingthe first dielectric layer 124. This process is then repeated to formthe conductive layer 126, the second dielectric layer 128, and the UBM120 of the WLCSP 100. Alternatively, the first dielectric layer 124, theconductive layer 126, the second dielectric layer 128, and the UBMs 120of the WLCSP 100 may be formed using a flip chip process.

FIGS. 2A-2C are directed to alternative embodiments of a WLCSP 200, 300,400 having various thicknesses of a die in a package. The WLCSP 200includes a die 202 having a circle-shaped first surface 204 of a thickerportion 206, as shown in FIG. 2A. The thicker portion 206 has a greaterthickness in cross-section as compared to a thinner portion 208, whichsurrounds the thicker portion 206. The die 202 includes a surface 210between the thicker portion 206 and the thinner portion 208, which maybe angled due to processing steps.

The WLCSP 300 includes a die 302 having an oval-shaped first surface 304as shown FIG. 2B. The oval-shaped first surface 304 is a surface of thethickest part of the die 302, as measured from an active surface of thedie 302. A second surface 306 is a surface of the thinnest portion ofthe die 302.

The WLCSP 400 includes a die 402 that has a diamond-shaped first portion404 as shown in FIG. 2C. This first portion 404 is thicker than a secondportion 406, which surrounds the first portion 404. Corners or points408 of the first portion 404 are not aligned with corners 410 of the die402. Instead the corners 408 are aligned in a middle region of sides 412of the die 402. The alternative embodiment of the WLCSP 400 in FIG. 2Cwith the diamond-shaped first surface is similar to the embodimentdisclosed in FIG. 1A as discussed earlier, but in this alternativeembodiment of the WLCSP 400, the square-shaped first surface 110 isrotated with respect to the corners 410 of the die 402.

FIGS. 3A-3B are directed to an alternative embodiment of a WLCSP 500including a die 532, a first surface 510, a second surface 512, a thirdsurface 516, a fourth surface 514, first sidewalls 518, second sidewalls513, a plurality of UBMs 520, and a plurality of solder balls 522.

In this alternative embodiment, the first surface 510, the secondsurface 512, and the third surface 516 are opposite the fourth surface514. The first surface 510 is positioned at a center of the WLCSP 500.However, in alternative embodiments, the first surface 510 may be in adifferent position on the WLCSP 500. The first surface separates andcouples the second surface 512 to the third surface 516. The secondsurface extends between the first surface 510 and one of the firstsidewalls 518 of the plurality of sidewalls 513, 518. The third surface516 extends between the first surface 510 and another of the firstsidewalls 518 of the plurality of sidewalls 513, 518. The first surface510, the second surface 512, and the third surface 516 extend betweenone of the second sidewalls 513 and another of the second sidewalls 513.The first sidewalls 518 have a rectangular shape and the secondsidewalls 513 have a trapezoidal shape on a rectangular shape orotherwise a non-rectangular shape. However, in alternative embodiments,the first sidewalls 518 and the second sidewalls may have differentshapes. The second surface 512 and the third surface 516 are at anincline. The incline of the second surface 512 and the third surface 516may be the same or may be different.

The UBMs 520 are on the fourth surface 514. The solder balls 522 arecoupled to the UBMs 520 on the fourth surface 514. The die includes anRDL, not shown in these figures. Each respective solder ball 522 iscoupled to its own respective UBM 520. The solder balls 522 are utilizedto couple the WLCSP 500 to a PCB or to other electronic componentswithin an electronic device such as a smart phone, a tablet, a computer,a calculator, or any other similar electronic device. The plurality ofUBMs 520, which may be a plurality of contact pads, bond pads, or someother electronic coupling location, and a plurality of solder balls 522are in a Ball Grid Array (BGA) configuration on the fourth surface 514.The plurality of solder balls 522 are coupled to the plurality of UBMs520. Each respective solder ball 522 of the plurality of solder balls522 is coupled to a respective UBM 520 of the plurality of UBMs 520. TheUBMs 520 couple the WLCSP 500 and the die 532 of the WLCSP 500electrically and physically to other electronic components orsemiconductor devices.

The WLCSP 500 has a first thickness T1 that extends between the firstsurface 510 and fourth surface 514, the first thickness T1 is aconsistent thickness that remains the same at any location positionedbetween the first surface 510 and the fourth surface 514. The WLCSP 500has a second thickness T2 that extends between the second surface 512and the fourth surface 514. The second thickness T2 is a varyingthickness that varies between a first height H1 of the sidewalls 518 andthe first thickness T1. The WLCSP 500 has a third thickness T3 thatextends between the third surface 516 and the fourth surface 514, thethird thickness T3 is a varying thickness that varies between the firstheight H1 of the first sidewalls 518 and the first thickness T1. Thesurfaces 510, 512, 514, 516 and the thicknesses T1, T2, T3 of the WLCSP500 define a plurality of portions of the WLCSP 500.

The plurality of portions 525, 527, 529 includes a first portion 525, asecond portion 527, and a third portion 529. The first portion 525 islocated between the first surface 510 and the fourth surface 514 and hasthe first thickness T1. The second portion 527 is located between thesecond surface 512 and the fourth surface 514 and has the secondthickness T2. The second thickness T2 reduces in thickness as the secondportion 527 of the WLCSP 500 extends from the first portion 525 towardthe first sidewalls 518. The third portion 529 is located between thethird surface 516 and the fourth surface 514 and has a third thicknessT3. The third thickness T3 reduces in thickness as the third portion 529extends from the first portion 525 toward the first sidewalls 518.

The first sidewalls 518 have a first height H1. The first thickness T1is greater than the first height H1 of the first sidewalls 518. Thefirst portion 525 separates and couples the second portion 527 to thethird portion 529. The second portion 527 and the third portion 529 areadjacent to the first portion 525. The second thickness T2 of the secondportion 527 and the third thickness T3 of the third portion 529 arevariable thicknesses as discussed above. As the second portion 527extends toward the first sidewalls 518, the second thickness T2 variesbetween the first thickness T1 of the first portion 525 and the firstheight H1 of the first sidewalls 518. As the third portion 529 extendstoward the first sidewalls, the third thickness T3 varies between thefirst thickness T1 of the first portion 525 and the first height H1 ofthe first sidewalls 518. The first portion 525 is positioned at thecenter of the die 532. The first portion 525 is a non-critical portionand the second portion 527 and the third portion 529 are criticalportions.

Similar to the embodiment in FIGS. 1A-1E, this alternative embodiment ofthe WLCSP 500 includes the die 532 with a bond pad 130. In addition, theWLCSP 500 includes the RDL, not shown in this alternative embodiment.The RDL includes a first dielectric layer between the die 532 and aconductive layer, a second dielectric layer positioned between theconductive layer and the UBMs 520, and the conductive layer positionedbetween the first and second dielectric layers. The configuration ofthese components is the same or very similar as discussed above withrespect to the RDL of FIG. 1E and as shown in FIG. 1E.

In another alternative embodiment, the WLCSP 500 may not have sidewalls518, but instead, the second surface 512 and the third surface 516 mayextend from the first surface 510 and an edge of the WLCSP 500 that doesnot have the sidewalls 518. In other words, where a respective secondsurface 614 meets the third surface forms an edge of the WLCSP 600.

FIG. 4 is directed to another alternative embodiment of a WLCSP 600. TheWLCSP 600 includes a die 632 having a first surface 610, a plurality ofsecond surfaces 614, a third surface opposite the first and secondsurfaces (not shown), and a plurality of sidewalls 612.

The first surface 610 and the plurality of second surfaces 614 areopposite the third surface, which cannot be seen but is similar to thethird surface 114 in FIGS. 1B and 1E. The first surface 610 and theplurality of second surfaces 614 make up a back side surface, which is apassive surface. The third surface makes up a front side surface, whichis an active surface. The first surface 610 is positioned at the centerof the die 632 and has a square shape. However, in alternativeembodiments, the first surface may be a circle, an oval, a rectangle, orsome other shape as desired. Each of the respective second surfaces 614of the plurality of second surfaces 614 extends between the firstsurface and a respective sidewall of the plurality of sidewalls 612. Thesecond surfaces 614 surround the first surface 610 as shown in FIG. 4.In this alternative embodiment, the second surfaces 614 have atrapezoidal shape. However, in other alternative embodiments, the secondsurfaces may have a different shape. The second surfaces 614 are at anincline or otherwise vary in thickness between the first surface 610 andthe sidewalls. The incline is the same for each of the second surfaces614 in FIG. 4. However, in other alternative embodiments, the secondsurfaces may be at different inclines.

The WLCSP 600 has a first thickness that extends between the firstsurface 610 and the third surface, which, again, cannot be seen but issimilar to the third surface 114 in FIGS. 1B and 1E. The WLCSP 600includes second thicknesses, which are thicknesses that vary. The secondthicknesses extend between the second surfaces 614 and the thirdsurface. The first surface 610, the second surfaces 614, and the thirdsurface define a plurality of portions of the WLCSP 600. The pluralityof portions 625, 627 includes a first portion 625 and four secondportions 627 that surround the first portion 625. The first portion 625is located between the first surface 610 and the third surface and hasthe first thickness. The sidewalls 612 have a first height. The firstheight of the sidewalls 612 is less than the first thickness of thefirst portion 625. The second portions 627 surround the first portion625 and form a perimeter or boundary around the first portion 625. Thesecond portions 627 are located between a respective second surface 614of the plurality of second surfaces 614 and the third surface, and eachsecond portion 627 has a respective variable thickness of the secondthicknesses that varies between the first thickness of the first portion625 and the first height H1 of the sidewalls 612. The first portion 625is a non-critical portion 625 and the second portions 627 are criticalportions 627. This non-critical portion 625 and these critical portions627 also allow for the WLCSP 600 to be made even thinner.

In another alternative embodiment, the WLCSP 600 may not have sidewalls612, but instead, the second surfaces 614 may extend between the firstsurface 610 and an edge of the WLCSP 600 that does not have a sidewall.In other words, where a respective second surface 614 meets the thirdsurface forms an edge of the WLCSP 600.

Similar to the embodiment in FIGS. 1A-1E, this alternative embodiment ofthe WLCSP 600 includes the die 632 with a bond pad. In addition, theWLCSP 600 includes UBMs, solder balls, and an RDL having a firstdielectric layer and a second dielectric layer. The configuration ofthese components is the same as discussed above with respect to FIG. 1Eand as shown in FIG. 1E.

FIGS. 5A-5B are directed to another alternative embodiment of a WLCSP700. The WLCSP 700 includes a die 732 that includes a first surface 710,a plurality of second surfaces 712, a third surface 714 opposite thefirst surface 710 and the plurality of second surfaces 712. The die 732includes a plurality of fourth surfaces 716, a plurality of sidewalls718, a plurality of UBMs 720, and a plurality of solder balls 722. AnRDL is envisioned as appropriate, but not illustrated for simplicity.

In this alternative embodiment, the first surface 710, the secondsurfaces 712, and the fourth surfaces 716 are on an opposite side of thedie as compared to the third surface 714. The first surface 710 has aplus shape that is centered at a center of the die 732 as shown in FIG.5A. However, in other alternative embodiments, the plus shape of thefirst surface 710 may be off center or may be another shape. The fourthsurfaces 716 are vertical or otherwise transverse to the first surface710 and the second surfaces 712. However, in other alternativeembodiments, the fourth surface 716 may be at an incline. The secondsurfaces 712 are located at the corners of the WLCSP 700. The firstsurface 710, the second surfaces 712, and the fourth surfaces 716 makeup a back side surface of the WLCSP 700, which is a passive surface. Thethird surface 714 is a front side surface of the WLCSP 700, which is anactive surface.

The plurality of sidewalls 718 includes four sidewalls 718. The foursidewalls 718 are an upside down T-shape as illustrated. However, inother alternative embodiments, the sidewalls 718 may have a rectangularshape, a trapezoid shape, or some other shape. The first sidewall isopposite the second sidewall, and the third sidewall is opposite thefourth sidewall. However, in other alternative embodiments, a WLCSP mayhave any number of sidewalls or may have no sidewalls.

The WLCSP 700 has a first thickness T1 that extends between the firstsurface 710 and the third surface 714. The WLCSP 700 has a secondthickness T2 that extends between the second surfaces 712 and the fourthsurface 714. The second thickness T2 is less than the first thicknessT1. The surfaces 710, 712, 714 and thicknesses T1, T2 of the WLCSP 700define a plurality of portions 725, 727 of the WLCSP 700. The pluralityof portions 725, 727 includes a first portion 725 and a group of secondportions 727. The first portion 725 is located between the first surface710 and the third surface 714 and has the first thickness T1. The firstportion 725 extends from the first sidewall to the second sidewall, andthe first portion 725 extends from the third sidewall to the fourthsidewall. The second portions 727 are located between the secondsurfaces 712 and the third surface 714 and have the second thickness T2.The second portions 727 are positioned at the corners of the WLCSP 700.However, in other alternative embodiments, the second portions may havethicknesses that are all different, all the same, or any combination ofthicknesses or varying thicknesses. The first portion 725 is anon-critical portion 725 and the second portions 727 are criticalportions 727. These non-critical portions 725 and critical portions 727also allow for the WLCSP 700 to be made even thinner.

Similar to the embodiment in FIGS. 1A-1E, this alternative embodiment ofthe WLCSP 700 includes the die 732 with a bond pad. In addition, theWLCSP 700 includes the UBMS 720, the solder balls 722, and an RDL havinga first dielectric layer and a second dielectric layer. Theconfiguration of these components is the same as discussed above withrespect to FIG. 1E and as shown in FIG. 1E, even though the RDL is notillustrated in FIG. 5B for simplicity sake.

FIG. 6 is directed to another embodiment of a WLCSP 800. The WLCSP 800includes a die 832 that includes a plurality of first surfaces 810, asecond surface 812 that surrounds the plurality of first surfaces, athird surface opposite to the first and second surfaces 810, 812, aplurality of fourth surfaces 816 that extend between the plurality offirst surfaces 810 and the second surface 812, and a plurality ofsidewalls 818 that surround the other surfaces listed above.

The plurality of first surfaces 810, the second surface 812, and theplurality of fourth surfaces 816 are opposite the third surface, whichcannot be seen but is similar to the third surface 114 in FIGS. 1B and1E. The plurality of first surfaces 810, the second surface 812, and theplurality of fourth surfaces 816 make up a back side surface, which is apassive surface. The third surface makes up a front side surface, whichis an active surface. The plurality of first surfaces 810 are arrangedin an array of consistent shapes that are equally spaced from eachother. The first surfaces 810 of the plurality of first surfaces 810have a square shape. However, in other alternative embodiments, theplurality of first surfaces 810 may be arranged in a different formatthan the array shown in FIG. 6, and the first surfaces 810 of theplurality of first surfaces 810 may have a circular shape, oval shape,or a different shape. The second surface 812 surrounds each of the firstsurfaces 810 of the plurality of first surfaces 810. The plurality offourth surfaces 816 are vertical surfaces or otherwise transverse to thefirst surfaces 810 and the second surface 812. Each fourth surface 816extends between a respective first surface 810 of the plurality of firstsurfaces 810 and the second surface 812. However, in other alternativeembodiments, the fourth surfaces 816 may be at an incline. The firstsurfaces 810, the second surface 812, the third surface, and the fourthsurfaces 816 define portions of the WLCSP 800.

The WLCSP 800 includes a plurality of first portions 825 and a secondportion 827. These portions represent an area of semiconductor materialthat remains after a process to form different thicknesses on a passivesurface of a die or wafer. Each of the first portions 825 is locatedbetween a respective first surface 810 of the plurality of firstsurfaces 810 and the third surface. Each first portion 825 has a firstthickness that extends between the respective first surface 810 and thethird surface. The second portion 827 extends between the second surface812 and the third surface and has a second thickness that extendsbetween the second surface 812 and the third surface. The second portion827 surrounds each first portion 825. The first thickness of the firstportions 825 is greater than the second thickness of the second portion827. The second portion 827 is aligned with trenches, gaps, or spacesthat extend between the first portions 825. The first portions 825 arenon-critical portions 825 and the second portion 827 is a criticalportion 827. These non-critical portions 825 and this critical portion827 also allow for the WLCSP 800 to be made even thinner.

Similar to the embodiment in FIGS. 1A-1E, this alternative embodiment ofthe WLCSP 800 includes the die 832 with bond pads. In addition, theWLCSP 800 includes UBMS, solder balls, and an RDL on the third surface.The RDL includes a first dielectric layer and a second dielectric layer.The configuration of these components is the same as discussed abovewith respect to FIG. 1E and as shown in FIG. 1E, even though the RDL isnot illustrated in FIG. 6 for simplicity sake.

FIGS. 7 and 8A-8E are directed to a method of forming the WLCSPsdiscussed above. A first step 911 includes coupling a wafer to a tape.The wafer includes a plurality of die having active and passiveelectronic components arranged in a way to execute a desired process,such as sensing, processing, data storage, data transmission, or anyother suitable use for a die or chip. A second step 913 includes etchingthe wafer. The etching may be an isotropic etch, a anisotropic etch, ora combination of both. The etching may be a wet etch or a dry etch. Thisetching process results in the varying thicknesses of the variousembodiments of a WLCSP with varying thicknesses as discussed in thepresent disclosure. A third step 915 includes singulating the etchedwafer into WLCSPs. The etched wafer is singulated into WLCSPs utilizinga cutting device 943. The cutting device 943 may be a laser, a saw, orsome other device capable cutting a wafer into WLCSPs. A fourth step 917includes removing the WLCSP from the tape 940. The removing the WLCSPfrom the tape may be accomplished by a pick and place process. However,while this flow chart includes several steps, in other alternativeembodiments, there may be more steps or fewer steps in manufacturing theembodiments of the WLCSP discussed above and other alternativeembodiments of a WLCSP.

FIGS. 8A-8B are directed to the first step 911 of coupling a wafer 932to a tape 940 or other support for the packaging process. The wafer 932includes a passive back side surface 901 opposite an active front sidesurface 914. Lateral side surfaces 918 separate the passive back sidesurface 901 from the active front side surface 914. A plurality of UBMs920 is on the active front side surface 914 of the wafer 932 and aplurality of solder balls 922 are coupled to the UBMs 920. In thisrepresentation, the wafer is processed to include an RDL (not shown)coupled to the UBMs and solder balls before the singulation. In otherembodiments, the RDL and other features may be formed after singulation.The RDL may include a first dielectric layer, a second dielectric layer,and a conductive layer. However, in other alternative embodiments, theRDL may include any number of conductive or non-conductive layers.

The wafer is coupled to an adhesive 942 of the tape 940. The tape 940may be a kapton tape, a copper tape, or some other carrier suitable tohold the wafer during this process. The adhesive may be a glue, a dieattach film, or some other adhesive material. The wafer 932 is coupledto the adhesive 942 of the tape 940 by placing the plurality of solderballs 922 in the adhesive 942 of the tape 940 as shown in FIG. 8B.However, in an alternative embodiment of this method, the wafer 932 maybe coupled to the adhesive 942, the solder balls 922 may be on theadhesive layer 942, or some other coupling technique may be utilized toattach the wafer 932 to the tape 940.

FIG. 8C is directed to second step 913 of etching the wafer 932 whereportions of the silicon or other semiconductive material of the waferare removed forming various shapes and thicknesses on the passive sideof the wafer. After the first etching step 913 the wafer 932 includesfirst surfaces 910, a second surface 912, and third surfaces 916 betweenthe first surfaces 910 and the second surface 912. In this embodiment,the third surfaces 916 are inclined surfaces 916. However, in otheralternative embodiments, the third surfaces 916 may be verticalsurfaces. The first surfaces 910, the second surface 912, and the thirdsurfaces 916 make up the back side surface, which is a passive surface.As described above, the etching can form a variety of shapes andpatterns to accommodate the underlying circuitry in the die (thecritical and non-critical portions).

The back side surface 901, which is the passive surface, having surfaces910, 912, 916 is opposite the front side surface 914, which is an activesurface. This first etching step 913 may include applying a maskmaterial to the back side 901 of the wafer. The mask may be aphotoresist mask, a hard mask, or some other type of mask materialutilized for etching the wafer 932 using some etching technique. Theetching technique may be an anisotropic etching, an isotropic etching, achemical etch, a radiation etch, a plasma etch, a water jet etch, orsome other type of etching technique. The mask defines portions of thewafer 932 to stay and to be removed during this etching step 913. Afterthe wafer 932 has been etched, the mask is then removed.

FIG. 8D is directed to the third step 915 of singulating the etchedwafer 932 into distinct WLCSPs. The wafer 932 may be singulated intoindividual WLCSPs by a cutting device 943. The cutting device 943 may bea saw, a laser, a water jet, or some other cutting device. On the otherhand, the wafer 932 may be singulated into individual WLCSPs by a secondetching step. If a second etching step is used, a second mask may beapplied to the wafer 932 and then the wafer 932 is etched again. Thissecond etching step, which is to singulate the wafer 932 into individualWLCSPs, may be an anisotropic etching, an isotropic etching, a chemicaletching, a water jet etching, a plasma etch, a radiation etch, or someother type of etching technique. After this second etching step iscomplete, the second mask would be removed.

FIG. 8E is directed to the fourth step 917 of removing the WLCSPs fromthe tape 940. In this removal step 917, the individual WLCSPs areremoved from the adhesive 942 of the tape 940. At this point, the WLCSPsare ready to be further processed or shipped.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A device, comprising: a die including: a first surface, a secondsurface, and a third surface, the third surface being opposite the firstsurface and the second surface; a first portion having a first thicknessthat extends from the third surface to the first surface; and a secondportion extending from the first portion, the second portion having asecond varying thickness that extends from the third surface to thesecond surface.
 2. The device of claim 1, further comprising sidewallswith a first height.
 3. The device of claim 1, further comprising: afourth surface opposite the third surface; and a third portion extendingfrom the first portion, the third portion being spaced from the secondportion by the first portion, the third portion having a third varyingthickness that extends from the third surface to the fourth surface. 4.The device of claim 1, wherein the first surface is positioned at acenter of the die.
 5. The device of claim 2, wherein the sidewallsfurther include: a first sidewall with a rectangular shape; and a secondsidewall with a trapezoidal shape on a rectangular shape, the secondsidewall being transverse the first sidewall.
 6. The device of claim 5,wherein the first sidewall has a first length and the second sidewallhas a second length, the second length being greater than the firstlength.
 7. The device of claim 1, wherein the third surface of the dieincludes a plurality of contact pads and a plurality of solder ballscoupled to the plurality of contact pads.
 8. A device, comprising: afirst surface, a second surface, and a third surface, the third surfacebeing opposite the first surface and the second surface; a first portionpositioned at a center of a die having a first thickness, the firstthickness extending between the first surface and the third surface; anda second portion having a second thickness that is less than the firstthickness, the second thickness extending between the second surface andthe third surface, the second portion surrounding the first portion. 9.The device of claim 7, further comprising a plurality of third portions.10. The device of claim 7, further comprising: a fourth surface, thefourth surface being opposite to the third surface, the fourth surfaceextending from the first surface to the second surface; and a thirdportion having a third thickness, the third thickness extending betweenthe fourth surface and the third surface, the third thickness varyingbetween the first thickness and the second thickness.
 11. The device ofclaim 10, wherein the third portion surrounds the first portion.
 12. Thedevice of claim 10, wherein the third portion separates the firstportion from the second portion and couples the first portion to thesecond portion.
 13. The device of claim 10, wherein the fourth surfaceis at an incline.
 14. The device of claim 10, wherein a plurality ofcontact pads are on the third surface of the die and a plurality ofsolder balls are coupled to the plurality of contact pads.
 15. A device,comprising: a substrate including: a plurality of sidewalls; a firstportion having a first thickness, the first portion being centrallypositioned on the substrate; and a second portion having a secondthickness that is less than the first thickness, the second portionextending away from the first portion to at least one of the sidewalls.16. The device of claim 15, wherein the first portion and the secondportion are separated by a third portion, the third portion coupling thefirst portion to the second portion.
 17. The device of claim 16, whereinthe third portion includes an inclined surface that extends from thefirst portion to the second portion.
 18. The device of claim 17, whereinthe inclined surface has a trapezoidal shape.
 19. The device of claim15, wherein the second portion includes an inclined surface that extendsfrom the first portion to at least one of the sidewalls.
 20. The deviceof claim 19, wherein the inclined surface has a trapezoidal shape.